Method for the extrusion of thermoplastic foam

Claim 1

IN A METHOD FOR THE PREPARATION OF A GENERALLY RECTANGULAR FORMED SYNTHETIC RESINOUS THERMOPLASTIC BODY BY THE EXTRUSION OF A HEAT PLASTIFIED FOAMABLE GEL THROUGH AN ELONGATE ORIFICE INTO A REGION BETWEEN A PAIR OF SPACED APART GENERALLY PARALLEL RESTRAINING MEANS AND COOLING THE FOAM TO A GENERALLY SELF-SUPPORTING CONDITION WHICH SHOWS SHALLOW VALLEYS OR DEPRESSIONS EXTENDING IN THE DIRECTION OF EXTRUSION DUE TO COLLAPSING OF THE FOAM, THE IMPROVEMENT WHICH COMPRISES RESTRAINING THE FOAM DURING EXPANSION AT A LOCATION GENERALLY ADJACENT THE DIE AND AT ENDS OF THE EXTRUSION ORIFICE IN A CURVILINEAR PATTERN, THE PATTERN HAVING A MAXIMUM WIDTH OF FROM ABOUT 1.2 TO ABOUT 3 TIMES THE WIDTH OF THE DIE ORIFICE, THE EDGE RESTRAINING MEANS BEING GENERALLY DIVERGENT AWAY FROM THE EXTRUSION ORIFICE AND TOWARDS THE GENERALLY PARALLEL RESTRAINING MEANS WITH THE FURTHER LIMITATION THAT THE FOAM AT A LOCATION GENERALLY ADJACENT THE DIE IS RESTRAINED TO PROVIDE A GENERALLY CONCAVE EDGE TO THE INITIALLY EXTRUDED FOAM, AND SUBSEQUENTLY EXPANDING THE EXTRUDED GEL TO A DESIRED CONFIGURATION HAVING A GENERALLY RECTANGULAR CROSS-SECTION TO THEREBY PROVIDE A FOAM EXTRUDE OF IMPROVED DENSITY UNIFORMITY AND WITHOUT APPARENT COLLAPSE OF THE FOAM.